The interior of steam turbine housings are comprised, at least in part, of secured surfaces in the form sealing ribs. These ribs are formed on the surface of arcuate members that are secured to the interior of the housing so that when fully constructed, circumferentially extending seals are formed about the turbine housing and between the stage diaphragms thereof. The ribs are comprised of radially inwardly extending members, usually exhibiting a tapering cross-section which terminates at a sharp arcuate interior edge. These edges wear down in use as high pressure steam passes over them and occasionally the wear is non-uniform. Accordingly, the edges must, on occasion, be reconditioned. In the past such reconditioning has been done by a hand operation where the interior arcuate edge is hand scraped. Since this scraping process involves the reshaping of a plurality of arcuate ribs or teeth, each of the plurality of teeth needs to be reshaped in a uniform manner so that when the packings are used, high pressure steam will pass over the seals uniformly. Accordingly, correct flow of fluids through the turbine requires these sealing teeth or ribs to be at the same heights. To the extent reshaping, reconditioning or wear is non-uniform, the flow of fluid through the turbine will be adversely affected. Further, proper clearance between the seals and the various turbine stages is essential. Unless proper clearance of these seals between turbine stage diagrams is maintained, steam will leak through and along the shaft from the higher to lower pressure stages of the turbine resulting in lost efficiency.
The current method of reconditioning, reshaping or reforming these arcuate edges by hand typically requires a mechanic to lock a section of the packing in a bench vice and then, with a handheld cutter or scraper, make successive scrapes or cuts along each arcuate tooth edge in the packing. It is, of course, very difficult to accurately gauge how much hand cutting or shaping will provide a consistent and uniform tooth shape. However, in an attempt to provide some degree of control, the mechanic will use a hand held scale to try and determine, on a periodic basis at least, how much had actually removed from each tooth and to gauge how much to remove to have each tooth at an equal height.
There can only be limited control over a hand-held scraping device and it is often very possible to alternate between light and heavy strokes or cuts. The top edge of the tooth is thin and under alternating pressure conditions or because of lateral pressure the top edge may tear away allowing the cutter to slip off the tooth. This will clearly damage that tooth and its edge and perhaps the entire packer segment. To repair such a broken tooth or teeth and to have all teeth in the completed installed ring formed from the segments reshaped at uniform heights, would then require a great amount of additional hand effort and more frequent checking of tooth heights. Packing teeth resulting from this hand shaping also have razor sharp edges which could result in injury to the mechanic in those instances where a packing tooth would break and the cutter slipped.
Another problem with the hand shaping concerns the use of a cutter style where a wire edge is formed at the peak of each tooth. The formation of such a wire edge not only makes it more difficult to measure exactly how much material was being cut away, as the wire edge may or may not roll over or collapse when the measuring device was tightened in place, it might break off during measuring or worse it might break off after the seal was installed in the turbine.
Such control difficulties in the use of hand held cutting tool made accurate cutting difficult, provided little control over the actual depth of cut and resulted in improper clearances between the finished scraped segments. Further, the arc when scraped could be inconsistent, and it was difficult to obtain the desirable level of repeatability in the reconditioning process from tooth to tooth as well as from segment to segment. All of this might as well result in either improper clearances, or in service problems associated with misshapen or non-uniformly reshaped teeth.
I am aware of several devices used to clean the doors of coke ovens that use a pivoting type of scraping element as in Lindgren, U.S. Pat. No. 3,990,948, Jorzenink et al., U.S. Pat. No. 4,135,987, McCullough, U.S. Pat. No. 3,696,004 and Stanke et al., U.S. Pat. No. 3,741,806. However, none of these devices suggest the present invention nor do they suggest either the structure of the device and its mounting means, nor do they suggest how to accurately cut and recondition the arcuate edge of teeth in packing sections used in turbines.
Armstrong et al., U.S. Pat. No. 3,621,506 shows a device for scraping the interior of conduits or cylindrical sleeves wherein two scraper blades are mounted oppositely from one another on the opposite sides of a central mounting shaft with the cutting blades themselves supported by a plurality of springs, with cutting occuring when the shaft is rotated.